This invention relates to a silencer combined with a catalytic converter apt to convert the exhaust gases originating from internal combustion engines of any type into less harmful gases.
The harmful effects of exhaust gases discharged into the atmosphere by internal combustion engines has been evidenced since many years and the rapid increase in the number of motor vehicles in circulation has compelled the more industrialized countries to issue restrictive measures aimed at minimizing the emission of carbon monoxide, unburnt hydrocarbons and nitrogen oxide. As a consequence, catalysts have been developed which, when distributed over a large surface in contact with the exhaust gas stream, are suitable for converting these very polluting agents into substantially harmless gases, such as carbon dioxide, water vapour and nitrogen. On grounds of this knowledge, various kinds of catalytic converters to be fitted upstream of the conventional silencers have been developed and marketed.
These converters, however, present various problems such as the duration of their chemical efficiency related to the mechanical lifetime of their structure and to the complexity of the structure itself which lead to very high costs as well as to installation difficulties.
Whilst, in future, as a rule, vehicles will have to be factory-fitted with exhaust cleaners, the cost of the latter hampers both the installation on new vehicles and the conversion of the enormous number of already existing vehicles.
Catalytic converter-mufflers are already known in the art. For instance, U.S. Pat. No. 3,649,213 describes a catalytic converter-muffler device having a V-shaped bed configuration providing optimum gas flow characteristics and minimization of differential expansion problems from high-temperature conditions. A preferred unit has an oval outer chamber, a catalyst reservoir section, and curved sidewalls for the internal catalyst retaining screens so as to preclude buckling which occurs with flat plate members.
A combination muffler and catalytic converter having low back pressure is disclosed in U.S. Pat. No. 4,094,645. The device incorporates a venturi in the exhaust gas inlet path to add secondary air. The efficiency of the venturi is quite high since back pressures introduced downstream of the venturi are kept low by providing an extremely long outlet cone for the venturi which reverses the flow direction while preventing wall separation and turbulence. Sound attenuation is provided upstream of the venturi where the back pressures produced have a minimum effect in reducing venturi efficiency.
A housing for a catalytic medium supported on a metal foil and a catalytic converter containing such supported catalytic medium is described in EP-A-0263893. The catalytic converters are said to be especially useful for internal combustion engines whether spark ignited or compression ignited and especially for automotive vehicles.
An apparatus for catalytic or other purification of exhaust gases of internal combustion engines, with two exhaust gas treating bodies and a protection ring between them, is disclosed in EP-A-0387422.
None of these prior art devices anticipate the specific design of the converter-silencer of the instant invention.